OBJECTIVE: Maternal enterovirus infections during pregnancy have been linked to an increased risk of type 1 diabetes in the offspring. The aim of this study was to evaluate this association in a unique series of pregnant mothers whose child progressed to clinical type 1 diabetes. RESEARCH DESIGN AND METHODS: Maternal and in utero enterovirus infections were studied in 171 offspring who presented with type 1 diabetes before the age of 11 years and in 316 control subjects matched for date and place of birth, sex, and HLA-DQ risk alleles for diabetes. Acute enterovirus infections were diagnosed by increases in enterovirus IgG and IgM in samples taken from the mother at the end of the first trimester of pregnancy and cord blood samples taken at delivery. RESULTS: Signs of maternal enterovirus infection were observed in altogether 19.3% of the mothers of affected children and in 12.0% of the mothers of control children (P = 0.038). This difference was seen in different HLA risk groups and in both sexes of the offspring, and it was unrelated to the age of the child at the diagnosis of diabetes or the age of the mother at delivery. CONCLUSIONS: These results suggest that an enterovirus infection during pregnancy is not a major risk factor for type 1 diabetes in childhood but may play a role in some susceptible subjects.